Some properties of hardened cement paste and reinforcing bars upon cooling from elevated temperatures

Abstract

The post-cooling properties of reinforced concrete constituents are of great relevance in the assessment of a structure for re-use after fire. The expansive rehydration of dissociated calcium hydroxide on post-cooling exposure to air can cause a total loss in strength if cement paste specimens are heated to and maintained at 400°C or above. The use of cement replacement agents can mitigate this effect. The strength and ductility of hot-rolled mild steel and cold twisted steel on gradual cooling or quenching from various temperatures can be correlated with micro structural phenomena. There is a significant increase in strength and loss of ductility when both types of steel are quenched from temperatures above 723°C. Some practical implications of these properties are described, using examples of fire-damaged structures.